1. Field of the Invention
The invention relates to a calender roll heated by means of a heating medium in a liquid and/or gaseous state of matter, comprising a roll body provided with peripheral bores and is provided on both ends with flange journals provided with supply and discharge lines for the heating medium, and wherein the respective end areas of the peripheral bores are provided with thermal insulation bushings. Such calender rolls are commonly used, for example, for paper manufacture. The further development of the processes in the web manufacture, however, requires increasingly a more exact cylindricity of the heatable calender rolls as a result of changed temperatures and different web widths. In this connection, in particular thermally caused dimensional differences of a few μm can be the deciding factor in regard to the quality or even rejection of the product to be manufactured.
2. Description of the Related Art
It has been attempted to compensate shape errors of the heatable calender rolls, which result from the mechanical bending and from areas of different temperatures, by means of bending compensation rolls (multizone rolls). However, this has only been successful as long as the shape errors have a relatively long wave length and the correction potential of the bending compensation roll is sufficient. On the other hand, in the case of heatable calender rolls it has been attempted to control the heat introduction into the roll bodies with different thermal insulations. Also, the targeted temperature adjustment or insulation of the journal flanges for compensation of errors is known. Frequently, the opening areas of the peripheral bores are provided with fixedly mounted thermal insulation bushings in order to reduce the heat transfer into the end areas of the roll bodies and thus across the areas which are used by the web width.